Separate pacmacs.el into smaller modules

[rexim]

Extracted from #160 (comment)

@ForNeVeR: Overall I'd say that the pacmacs.el is getting huge, so maybe you need more modules here.

I'd suggest to move all the object management code to one file, state management to another, and (that's the most important part) emacs environment interoperation (such as input management and rendering) to the third file. It will make it more easy to create a server implementation in future. #37